Bismuth Overlayer Formation on GaAs(110)
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BISMUTH OVERIAYER FORMATION ON GaAs(110) S.-L. Chang, T. Guo, W.IK Ford, A. Bowler, and E.S. Hood Advanced Materials Center and the Departments of Physics and Chemistry, Montana State University, Bozeman, MT 59715
ABSTRACT The temperature and coverage dependent ordering of bismuth overlayers on GaAs(110) is examined using low energy electron diffraction (LEED). Sixth order electron diffraction profiles associated with overlayer ordering are observed at coverages of 0.7, 1.0, and 1.5 monolayers (ML) and for temperatures ranging from -110 C to 200 C. The full-width at half-maxima (FWHM) of the sixth-order spots are examined. Profile analysis reveals narrowing widths with increasing annealing temperature, indicating an improvement of the long-range ordering of the overlayers. Differences in inter- and intrachain ordering are observed, analyzed, and discussed. INTRODUCTION An understanding of the microscopic formation of metal overlayers on III-V semiconductor surfaces provides valuable insight to a variety of complex metalsemiconductor interface phenomena, e.g., Schottky barrier formation and Fermi level pinning. Not only are the atomic structure, electronic states, and the chemical bonding at the interface important properties that must be characterized, but so is the description of the interface growth kinetics. Antimony on GaAs(110) is one of the interface systems that has been investigated most intensively [1-4]. LEED proved that antimony forms ordered (lxi) overlayers when deposited at room temperature on a GaAs(110) surface up to one monolayer [4]. Antimony atoms bond to the underlying gallium and arsenic atoms by forming linear zigzag chains along the [110] direction [3]. Thermal desorption studies established that the first monolayer is stable against thermal annealing to about 550 C and that the growth mode is Stransky-Kranstanov (SK) [4]. Overlayers formed of bismuth, isoelectronic to antimony, on the III-V (110) surfaces are very little studied. High-resolution photoelectron spectroscopy results of bismuth on GaAs(110) indicated that a modified SK growth mode occurs for coverages up to two monolayers and a three-dimensional island growth occurs at higher coverage [5]. The desorption temperature for the first monolayer was reported to be above 350 C. Scanning tunneling microscopy (STM) results also show two-dimensional layer-by-layer growth for up to one monolayer [6]. Near one monolayer coverage the STM observed chains of bismuth atoms formed along the [110] direction with a typical length 24 A. These chains are interrupted by a missing bismuth atom due to the larger atomic radii of bismuth compared to that of the antimony. Two LEED studies of the growth of bismuth overlayers on GaAs(110) prepared at room temperature have been reported which support the SK growth model. The results obtained give evidence of sixth order periodicity in the diffraction and determine the detailed geometry of the adatom chains [7,81. In this paper, we present a study of the temperature- and coverage-dependent growth kinetics us
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